标题： 从极端质量比双星到非定态引力波背景 显示英文标题

标题： From eccentric binaries to nonstationary gravitational wave backgrounds

摘要： 宇宙中大量发射引力波（GW）的双星系统会产生一种随机噪声，称为引力波背景（GWB）。 GWB的特性直接依赖于其组成部分的属性。 如果双星系统处于偏心轨道中，已经明确的是它们辐射的引力波功率强烈依赖于其瞬时轨道相位。 因此，它们的功率谱会随时间变化，导致产生的GWB表现出非平稳性。 在这项工作中，我们估计了作为双星偏心率函数的GWB功率谱的时间相关波动幅度。 具体来说，我们关注由脉冲星计时阵列（PTA）应能观测到的超大质量黑洞双星（SMBHB）群体产生的GWB。 我们表明，均匀分布的大规模等质量SMBHB群体产生了一些无法被当前PTA数据集检测到的非平稳特征。 然而，使用更现实且天体物理上合理的SMBHB群体，我们表明这种非平稳性可能会变得非常显著且可检测，特别是在更大质量和更偏心的群体情况下。 特别是，当一个双星稍微比GWB亮一些时，我们证明了时间波动可能变得显著。 对于相对于GWB具有低信噪比（SNR）的单个双星系统（SNR$\approx$1），这也是正确的，标准数据分析方法难以检测到这些系统。 在GWB中检测到非平稳特征可能表明存在一些相对较亮的处于偏心轨道上的引力波源，这为我们提供了解信号起源的新见解。 显示英文摘要

摘要： A large population of binary systems in the Universe emitting gravitational waves (GW) would produce a stochastic noise, known as the gravitational wave background (GWB). The properties of the GWB directly depend on the attributes of its constituents. If the binary systems are in eccentric orbits, it is well established that the GW power they radiate strongly depends on their instantaneous orbital phase. Consequently, their power spectrum varies over time, and the resulting GWB can appear nonstationary. In this work, we estimate the amplitude of time-dependent fluctuations in the GWB power spectrum as a function of the eccentricity of the binaries. Specifically, we focus on the GWB produced by a population of supermassive black hole binaries (SMBHB) that should be observable by pulsar timing arrays (PTA). We show that a large population of homogeneously distributed equal SMBHBs produces nonstationary features that are undetectable by current PTA datasets. However, using more realistic and astrophysically motivated populations of SMBHBs, we show that the nonstationarity might become very large and detectable, especially in the case of more massive and eccentric populations. In particular, when one binary is slightly brighter than the GWB, we demonstrate that time fluctuations can become significant. This is also true for individual binary systems with a low signal-to-noise ratio (SNR) relative to the GWB (SNR $\approx$ 1), which standard data analysis methods would struggle to detect. The detection of nonstationary features in the GWB could indicate the presence of some relatively bright GW sources in eccentric orbits, offering new insights into the origins of the signal.